The highest performance Si power diodes are Si Schottky diodes. Si Schottky diodes have low reverse recovery time compared to other types of Si power diodes, and also have the lowest forward voltage drop (0.4V to 0.3V). While Si Schottky diodes have the advantage of low forward losses and negligible switching losses compared to other diode technologies, the narrow bandgap of silicon limits their use to a maximum voltage of around 200 V. Power diodes with a breakdown voltage significantly above 200V have been realized by cascading a low-voltage Si Schottky diode with a high-voltage AlGaN/GaN HEMT (high electron mobility transistor). Such a cascaded diode has the low threshold voltage benefit of a Si Schottky diode and the high current density benefit of GaN.
The functionality of the cascaded diode is given by the Si Schottky diode causing a potential increase in the reverse direction until pinch-off of the high-voltage HEMT (the HEMT is a normally-on device in this case). Without this minimum bias on the cathode side of the Si Schottky diode, the high-voltage HEMT is switched on. As such, the overall switching speed of the cascaded diode can benefit from the high-voltage HEMT and from the fast Si Schottky diode. However, conventional cascaded diodes implement the low-voltage Si Schottky diode and the high-voltage HEMT on two separate dies (chips), one die including the high-voltage GaN HEMT and the other die include the low-voltage Si Schottky diode. The two dies are combined via a common package including bonding or clip connections between the dies. These connections in the package cause unwanted parasitic inductances and capacitances which degrade the dynamic behavior of the overall cascade circuit.